The present invention relates to an airbag device for a driver which is installed in a steering wheel of an automobile and more particularly to an airbag device for a driver in which a horn switch is arranged on a hidden side of an occupant-facing portion of a module cover of the airbag device.
An airbag device for a driver comprises an inflator, an airbag, a retainer to which the inflator and the airbag are attached, and a module cover for covering the airbag. The module cover is provided with a tear line. When the inflator is actuated to inflate the airbag, the module cover is torn along the tear line so that the airbag is deployed into a vehicle cabin. When the module cover is torn along the tear line, a flap like a tongue is formed in the module cover and the flap opens into the vehicle cabin.
In one of the driver airbag devices, a horn switch is arranged on the hidden side of an occupant-facing portion of the module cover, so that depressing the occupant-facing portion of the module cover sounds the vehicle horn. An airbag device disclosed in Japanese patent publications 8-188109 and 9-66793 has a horn switch in a form of a sheet or a membrane and a plate for supporting the switch which are arranged on a hidden side of a module cover, whereby the horn switch is actuated just by lightly depressing the module cover. The plate extends over the entire area on the hidden side of the occupant-facing portion of the module cover and both sides of the backing plate are supported by the retainer so that the sheet switch for the horn is supported firmly by the plate. Since the supporting plate is disposed over a tear line of the module cover, the plate should be also provided with a tear line along the tear line formed in an occupant-facing portion of the module cover. When the airbag is inflated by gases spouted from the inflator, the airbag should tear not only the module cover but also the plate along the respective tear lines. As a result thereof the inflator employed in the airbag device of this type should have high pressure for generating gas.
If the supporting plate is arranged within a range of one of the tongue-like flaps defined by the tear line of the occupant-facing portion of the module cover, the plate is not required to have the tear line. In this case, however, since the plate is held by the retainer only at one end thereof, that is, in the cantilevered state, the plate is easily moved backward together with the sheet switch when the switch is depressed so that it is necessary for actuation of the sheet switch to depress the occupant-facing portion of the module cover with relatively strong force.